JEE Main · 2019 · 08 Apr 2019 · Shift 2 · General Principles and Processes of Isolation of Metals

The Mond process purifies nickel. Impure nickel is warmed with carbon monoxide at about $330$ to $350\text{K}$ to form the volatile carbonyl, $\mathrm{Ni}+4\mathrm{CO}\to \mathrm{Ni}(\mathrm{CO}){}_4$, which carries the nickel off as a gas, away from the impurities. Heating that vapour more strongly, to about $450$ to $470\text{K}$, reverses the step, $\mathrm{Ni}(\mathrm{CO}){}_4\to \mathrm{Ni}+4\mathrm{CO}$, depositing pure nickel. So the Mond process is used for the purification of nickel.